As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
SUBSTANTIAL ENGINE VIBRATION REPORTED BY PILOT DURING FLIGHT. #4 CHT CONSISTENTLY ~40% HIGHER THAN OTHER CYLINDERS. MAG CHECKS NORMAL. VIBRATION REMAINED THE SAME REGARDLESS OF MAGS SELECTED. OIL PRESSURE AND TEMP REMAINED IN GREEN. PERFORMED COMPRESSION CHECK ON #4 CYLINDER. #4 CYLINDER COMPRESSION IS 0/80. UPON FURTHER INSPECTION FOUND THAT THE #4 CYLINDER HEAD IS CRACKED.